This application claims the priority of German Application No. 10 2004 037 104.0 filed Jul. 30, 2004, the disclosure of which is expressly incorporated by reference herein.
This invention relates to a hydraulic linear drive. Preferred embodiments of the invention relate to a hydraulic linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged to be longitudinally displaceable in a cylinder housing and to subdivide the cylinder housing space into at least two pressure spaces which can receive hydraulic oil through control lines, and a shift valve operable to control optional pressure action on the two pressure spaces.
Hydraulic linear drives are used in automatic transmissions, for example, for synchronizing the gears (see, for example, Johannes Loomann, Zahnradgetriebe [Gear Wheels], 2nd edition, pages 156 ff.).
With the generic hydraulic linear drives, the double piston bordered by two pressure spaces is displaced accordingly to the left or right by a pressure action, as described and explained in DE 198 34 955 A1 corresponding to U.S. Pat. No. 6,295,810, for example, the rate of adjustment of the hydraulic piston is adjustable through additional control valves integrated into the two control lines.
An object of this invention is to provide a circuit arrangement with which the adjusting force and/or adjusting speed of the double-acting hydraulic cylinder can be varied easily with only a few hydraulic components. This object is achieved according to certain preferred embodiments of the invention by providing a hydraulic linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged to be longitudinally displaceable in a cylinder housing and to subdivide the cylinder housing space into at least two pressure spaces which can receive hydraulic oil through control lines, and a shift valve operable to control optional pressure action on the two pressure spaces, wherein a connecting line is provided between two control lines leading to the pressure spaces with a control valve for optionally releasing or blocking the connecting line.
Due to the fact that a connecting line in which a control valve optionally either releases or blocks the connecting line is provided between the two control lines leading to the pressure spaces, the volume flow to the pressure space acted upon by the pressure is controllable so that the adjusting rate and/or adjusting force of the hydraulic piston can be influenced in this way. For example, when using the linear drive as a hydraulic transmission actuator, a reduction in the synchronous force is possible. If comfortable shifting is desired, then the gear may be engaged with a low adjusting force whereas if a sporty shifting style is desired, the transmission actuator can be operated with a high synchronous force.
Other advantageous embodiments and refinements of the hydraulic linear drive are achieved through the features described herein and in the claims.
The control valve which is integrated into the connecting line has three shift positions in a first advantageous embodiment; in a first shift position, the connecting line is closed; in a second shift position, the connecting line is opened with a small opening cross section and in a third shift position it is opened with a larger opening cross section. In addition to the three discrete shift positions described above, it is also contemplated for the control valve to have an adjustable valve element which is continuously adjustable between a completely open shift position and a completely closed shift position.
In a further advantageous embodiment, the control valve has a first closed shift position and a second open shift position, whereby the control valve can be operated in cycles between these two shift positions. In this way it is also possible to vary the volume flow to the pressure chamber which is acted upon by hydraulic oil and thus to vary the adjusting force acting on the hydraulic piston.
Two exemplary embodiments of this invention are depicted in the drawing and described in greater detail below.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.